1. Field of the Invention
This invention relates to rotary die cutters adapted to punch a predetermined shape of cardboard from a cardboard sheet.
2. Description of the Prior Art
A rotary die cutter comprises a knife cylinder and an anvil cylinder which are arranged to oppose each other. The knife cylinder is provided with a punching blade and may also include a scoring blade adapted to score a line on the cardboard sheet. Conventionally the knife cylinder includes material such as plywood covering a portion of the cylinder and the knife, and scoring blade if employed, are mounted in this plywood. The anvil cylinder is usually provided with an outer peripheral surface constituting the anvil which is made of a material such as urethane. Both cylinders are adapted to be driven by means of two gears positioned at one end of each cylinder. In order that the punching blade not engage the same portion of the anvil in successive rotations of the anvil cylinder, the two gears have different numbers of teeth and further means are provided for effecting axial displacement of the anvil cylinder. In operation, as the cardboard sheet is inserted into the space between the two cylinders, the punching blade is driven into the anvil, effecting the punching of the desired shape from the cardboard sheet. In a conventional rotary die cutter impressions generated by the punching blade are not distributed uniformly over the anvil surface and the resultant concentration of damage to the anvil surface shortens the period of use before polishing or renewal of the anvil is required.
By the present invention an improved rotary die cutter is provided which overcomes this deficiency of prior art rotary die cutters and distributes the punching impressions widely over the anvil surface. Thereby the damage to the anvil surface from the punching impressions is not concentrated but is widely dispersed. This results in a longer anvil life and increases the time period which elapses before polishing or renewal of the anvil is required. The invention thus provides for easier maintenance and economy of operation.